Conventionally, X-ray CT apparatuses have increasingly carried out tomography called the dynamic scan. The dynamic scan is a technique for, after a contrast medium agent is administered, continuously performing scans over a predetermined time period depending upon a rate of the contrast medium agent flowing through an object.
A conventional X-ray CT apparatus generates a non-contrast image of an object in non-contrast, sets an ROI (region of interest) and a threshold based on the non-contrast image, and starts the injection of a contrast medium agent. After the start of the injection of the contrast medium agent, Real Prep starts. Real Prep is a function for sensing a timing of start (trigger) for a main scan such as a dynamic scan and starting the main scan when a CT value of the ROI exceeds the threshold.
In conventional ROI setting, merely an operator places an ROI on any position using a non-contrast image. Currently, however, Real Prep is used in various situations. For example, Real Prep is carried out while a patient is breathing, or a main scan is immediately performed once a contrast medium agent reaches a predetermined region. Furthermore, it is necessary to sense a timing to start a main scan with high accuracy. However, in the conventional arts, there is the case in which even if a high CT value region such as a bone or a calcified area is outside and around an ROI at the time of ROI setting that uses a non-contrast image, after Real Prep is started, the high CT value region may enter the ROI because of a heartbeat, breathing, or a body movement of an object. As a result, a timing to start a main scan may be mistaken.
A body movement of an object often involves up-and-down motions as well as forward, backward, right and left motions. Further, if Real Prep is carried out near a main artery aorta while an object is breathing, it is likely that up-and-down motions of the object cause a high CT value region such as a calcified area to enter an ROI.